It is known that in semiconductor spectrometers, a semiconductor detector and a field-effect transistor input stage of the preamplifier requires cooling to cryogenic temperature to lower the self-noises.
Known in the art are semiconductor spectrometers wherein the cooling is performed by solid or liquid cooling agents, such as solid methane or liquid nitrogen.
The systems used for storage and feeding the cooling agents are usually of a large size and must be continuously recharged, thus limiting the application to stationary laboratories. Such spectrometers are inconvenient for in-the-field research application even when cryostats adapted for shaft and well measurements are used. The quantity of the cooling agent stored is small and cannot be increased because of the restricted size of well devices.
Besides, when liquid cooling agents are used, the semiconductor spectrometer must be maintained in stringed orientation in order to avoid deterioration by contact between the cooling agent and the cold finger.
The overall dimensions of the spectrometer can be substantially decreased by using Peltier elements adapted for cooling the semiconductor detector and a field-effect transistor.
In this system, the semiconductor detector is fixed on a hollow heat conducting cylinder mounted on the cold junction of the Peltier element, and the field-effect transistor and a high-value resistor are arranged inside the cylinder.
The cooling of the detector system by Peltier elements has resulted in a more compact design of the semiconductor spectrometer. The external cooling is eliminated, and the semiconductor spectrometer has only an electric cable to provide greater flexibility and reliability in well applications.
Moreover, the semiconductor spectrometers are cooled by Peltier elements capable of orientation at any angle.
This detector system, however, fails to provide both an immediate heat contact of the semiconductor detector and the field-effect transistor with the cold junction of the Peltier element, and heat protection thereof against heat inputs produced by the case of the vacuum chamber, thus substantially increase their self-noises, and, in turn, result in loss of spectrometer performance.
Besides, the cooling of the cylinder results in additional energy consumption, thus increasing the overall power input.
Also known in the art are semiconductor spectrometers cooled by Peltier elements (cf. publication of the Institute of Nuclear Research in Poland).
Such a spectrometer comprises a vacuum chamber having an entrance window to pass radiation therethrough. In the interior of the chamber, there is arranged a thermoelectric cooler formed by a set of Peltier elements. Mounted on the cold side of the thermoelectric cooler is a heat conducting plate, and a semiconductor detector and a field-effect transistor is also fixed thereon. The hot side of the thermoelectric cooler is provided with a heat removing radiator.
The immediate heat contact of the semiconductor detector and of the field-effect transistor with the cold side of the thermoelectric cooler reduces their self-noises, thus enhancing the performance of the spectrometer as a whole.
In operation, the semiconductor detector requires maximum cooling but does not liberate heat, while the field-effect transistor requires less cooling but gives off heat, whereby a significant increase in power input of the thermoelectric cooler is essential to satisfy these contrary requirements.
The disadvantage of such a semiconductor spectrometer is the necessity of cooling the hot side of the the thermoelectric cooler by means of a refrigerant line to supply the additional external cooling agent, which, in turn, enlarges the size and weight of the spectrometer as a whole and fails to provide its self-sufficiency for field applications.